This invention relates to a spiral heat exchanger, particularly for fluids under high pressure and for use in chemical reactors. The heat exchanger is of the type which has sheet metal spirals which form at least two spiral flow channels for the fluids between which heat exchange is to take place. The spirals are arranged between two removable end plates which are pressed against the spirals by means of mounting bars and are provided with axially oriented inlet and outlet openings for one fluid, particularly the product fluid to be treated by the heat exchange, whereas the other fluid, such as a heating fluid or a refrigerant, is radially introduced into and removed from its spiral flow channel.
In spiral heat exchangers of the above-outlined type, particularly when used in reactors of chemical plants, one of the fluids flows through the spirals axially, while the other flows circumferentially therethrough. Guiding the fluids in such a "cross flow" has the disadvantage that the cross-sectional surface for the flow in the axial direction is disproportionately large as compared to the spiral flow and, as a result, the flow velocities of the axial fluid stream are very small, and consequently, the heat-transfer coefficient is low. Thus, even in case of a high heat-transfer coefficient on the other wall side, the overall heat transmission coefficient which is representative of the entire heat exchange is permanently reduced.
Apart from the above considerations, channelling the fluids in a cross flow is further undesirable for reasons of thermal technology, because significant differences in the temperature gradients of the two fluids appear.
It has been attempted to remedy the above disadvantages by arranging the heat exchanger externally of the chemical reactor and to circulate the product fluid by a circulating pump. Such a solution, however, involves significant expenses. Particularly in case the product is under a relatively high pressure of, for example, 30-40 bar, as it is the case in many hydrating reactions, the heat exchanger has to be of extremely stable construction to ensure the necessary pressure resistance.